Open with TextWrangler. In TextWrangler, Depending on your System Definitions, there will be a string that says either Mac Mini, Mac Pro, iMac Etc. You can change this to whatever you like. Anything in the Brackets are on Line 2 of About this Mac. I changed mine to "Mac Mega (Late 2012)"

As seen in this image, The Text "Mac Pro" is on the first row of About This Mac Overview Tab. In Brackets Early 2008.

Save and Close. If you want to see if it works, Close any About this Mac windows and reopen them. If no changes then reboot.

Move the copy to System/Library/CoreServices/Loginwindow.app/Contents/Resources/english.lproj/AboutThisMac.Strings

You should now see:

Part 3. More Specs!

Part 2 helped you modify the first About This Mac windows. When you click More info... then you'll see even more specs in another About this mac "Overview" window.

To change these specs, Navigate to /Applications/Utilities/System Information Show Package Contents /Contents/Resources/English.lproj/SPInfo.Strings Open with TextWrangler.

This file has several more specs you can modify. You can even go through and change the labels if you like. Ex Processor to CPU. I prefer not to do that.

To change the Processor Specs: Go to key MAC_CPU_TEXT
Currently the field is %1$@ %2$@

IF YOU WANT IT TO SAY Processor or Graphics or Whatever its supposed to say Leave in the "%1S@ " <--- Two Spaces There

After that You can change this to whatever, I changed mine to "%1S@ 3.59 GHz Intel Ivy Bridge Core i5" (Without Quotes) as that is what I have.

You may or may not need to restart for these settings to take place.

Part 4: Adding your own Mac Image to About This Mac

Now you can add your own Mac Case to the About This Mac "Overview" tab. I got the picture of my case from the place I bought it at, Microcenter. They had a decent shot of the front of the case which is what I used. Check to see if you can find your case online somewhere and use that pic, otherwise get out a camera

First thing to let you know of, You'll be replacing the image of whatever mac is in your About this Mac Overview Tab. This also replaces the image of other Macs on your network. For example I have two Mac Pros at home, If my system definitions was set to a Mac Pro then I would have to replace the image of the Mac Pro hense I would not see the same image of a Mac Pro on my network. Makes Sense? I hope so. If thats an issue change your system definitions to Mac Mini or iMac. Most people don't have 2 Mac Pros at Home, But I Do!

EDIT: One More thing, If you want you can edit the apple logo seen on the first About This Mac screen.

This is simply a PNG file located at:

System/Library/CoreServices/Loginwindow.app/contents/Resources/MacOSX.Png and MacOSX@2x.Png

Rename the orginals files with .bak at the end is case something happens.

Throw in your new Apple Logo and restart. If you like what I have you can download it in my Attachments. If you want to Make your own I suggest using
Charcoal Font. That I believe is Close to Apple's Font for OS 10. Myraid Pro was recommended as well!

UPDATE! Change Your Monitor's Name!

I know this isn't what I was exactly shooting for in this post, (Having two different monitor images) But I'm getting closer. I found out how to change the monitors name. So if your like me and have simply "Syncmaster" or "VA912-4SERIES" as your
About this Mac Displays monitor name, then you might want to change it. The change is quite simple.

Before

After

Following the original methods of this tutorial to Save and Edit files the change is located in /System/Library/Displays/Overrides/Contents/Resources/English.lproj/Localizable.strings

Open with Text Wrangler.

The point of this file is to tell the system when a monitor is plugged in called "Whatever" that is changes it from "Whatever" to "Dell Whatever"

For English this doesn't do a whole lot. The only difference here is "Unknown Display" is changed to "Display"

This file makes more sense for other languages. For Example The file will read "Color LCD" in english and Display it in Japanese as "カラー LCD"

However we can use this file to our advantage.

At the bottom of the file (Above </dict>) Type in:

<string>WHATEVER YOUR MONITOR IS CALLED NOW</string>
<key>WHATEVER YOU WANT IT TO BE CALLED</key>

You Find out what it called from About this mac Display Section. Copy the Name.
*Don't Copy the " Display" Part!